This invention relates generally to the field of data processing and more specifically to a method and system for data communications.
The rising use of asymmetric digital subscriber lines (ADSL) has led to the need for improved ADSL transceiver units. The high data rates required to properly support emerging multimedia Internet applications far exceed the capabilities of conventional voice band transceiver units. For example, seamless, real-time delivery of digital video clips might require connections up to 100 times faster than is currently available with voice band transceiver units. ADSL transceiver units (ATUs) provide residential Internet users with a much-needed solution to this shortage of remote access bandwidth, while taking advantage of the enormous installed base of copper twisted-pair telephone wire that exists between the telephone company central offices (COs) and local residential customers. ATUs connected directly to the Internet are installed in the telephone company central office, allowing remote access over the copper twisted-pair telephone lines by a remote ATU (ATU-R) in the home of a residential customer. The Internet data does not pass through the telephone switching network, and as a result the ADSL link can provide data communication rates in the Mbit/sec range.
An ATU and a plain old telephone service (POTS) telephone (or other voice band equipment) can in principle operate simultaneously over the same copper loop, since they use different frequency bands. The connection of a telephone to the same wires as an ATU, however, presents several problems that result from the fact that the telephone is not designed to handle high frequencies (above 3.5 kHz). Since these frequencies are beyond the voice band, telephones do not behave well in the presence of high power signals in frequency ranges above voice band. The telephone often contains nonlinear components, such as Zener diodes, transistors, varistors, triacs, and other devices used for over-voltage protection, side tone generation, and over-volume protection. When a telephone goes off-hook while transmission is in progress, these components produce nonlinear echoes at the harmonics of the upstream signal, the signal travelling from the remote transceiver to the central office. Some of these echoes lie in the downstream band of the ATU, thus severely corrupting the downstream signal, the signal travelling from the central office to the remote transceiver.
According to one known approach for resolving these problems, a POTS splitter is used to isolate the DSL high frequency signals from the voice band signal. Generally, a splitter is a combination of low-pass and high-pass filters. The low-pass filter is used to isolate the voice band signal and route it to and from the telephone, and the high-pass filter is used to isolate the DSL signal and route it to and from the ATU. The splitter may be part of the ATU. A problem with this approach is that the telephone has to be connected to the ATU. Alternatively, the splitter may be installed at the line drop to the home. A problem with this approach is that it requires professional installation and re-wiring of the telephone lines going to the ATU inside the customer""s premises.
According to another known approach, the ATU has one operating condition when a POTS device is on-hook and another operating condition when the device is off-hook. During off-hook operation, the power of the upstream signal is reduced to avoid the nonlinear regions of the nonlinear components in the POTS device, thus reducing the nonlinear echo and the generated harmonics. As a result, the POTS telephone and the ATU may be connected directly to the same line without a splitter, thus enabling the customer to plug the ATU as well as the telephone in any phone jack in the home. There is, however, a problem with the splitterless operation of ATUs. The power cutback of the upstream signal causes the central office ATU (ATU-C) to estimate that the ATU-R is at a greater distance from the ATU-C than it actually is. As a result, the ATU-C boosts its downstream output power. If the ATU-R is far away, then the received power level is within the operational range of the high gain receiver amplifier, and no problems result. If, however, the ATU-R is close to the ATU-C, then the received power level will saturate the amplifier and the connection will fail or perform poorly.
While these approaches have provided improvements over prior approaches, the challenges in the field of data processing have continued to increase with demands for more and better techniques having greater effectiveness.
In accordance with the present invention, a method and system for data communication are provided that substantially eliminate or reduce the disadvantages and problems associated with previously developed systems and methods.
According to one embodiment of the present invention, a system for data communication is disclosed that comprises a hybrid circuit that receives a signal. A switched gain circuit coupled to the hybrid circuit receives the signal from the hybrid circuit. A receiver circuit coupled to the switched gain circuit receives the signal from the switched gain circuit. The switched gain circuit adjusts the power of the signal transmitted to the receiver circuit. More specifically, the switched gain circuit detects the power of the signal received from the hybrid circuit, and adjusts the power of the signal transmitted to the receiver circuit based upon the power of the signal received from the hybrid circuit.
According to one embodiment of the present invention, a method for data communication is disclosed. A signal is received using a hybrid circuit. The signal is transmitted to a switched gain circuit coupled to the hybrid circuit. The power of the signal is adjusted using the switched gain circuit. The adjusted signal is transmitted to a receiver circuit coupled to the switched gain circuit. More specifically, the power of the signal is detected, and the power of the signal transmitted to the receiver circuit is adjusted based upon the power of the signal received from the hybrid circuit.
A technical advantage of the present invention is that it protects the receiver amplifier of an ADSL transceiver unit, which allows for power cutback of the upstream signal in order to avoid the nonlinear regions of the nonlinear components of a POTS device, thus reducing the nonlinear echo and the generated harmonics and improving signal quality. Another technical advantage of the present invention is that it allows a customer to plug the transceiver unit as well as a telephone in any phone jack on the customer""s premises, without requiring professional installation and rewiring of the telephone lines inside of the premises. These technical advantages provide residential users with a much-needed solution to the shortage of remote access bandwidth, while taking advantage of the enormous installed base of copper twisted-paired telephone wire that exists between central offices and local residential customers.
Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.